The embodiments herein generally relate to mobile television (TV) technologies, and, more particularly, to transmission schemes for mobile TV digital video broadcasting (DVB) applications.
Handheld devices with integrated digital television access are a relatively new phenomenon. Such technology has traditionally been limited by size, power consumption, and most importantly performance. Poor performance of such devices has typically been the result of the constantly changing receiver environment. More particularly, the quality of the received signal is affected by the device's ability to manage adjacent-channel rejection, low signal-to-noise ratios, and Doppler compensation, among other factors.
DVB-H is the specification for bringing broadcast services to handheld receivers, and was formally adopted as an ETSI (European Telecommunications Standards Institute) standard in November 2004. More specifically, DVB-H is a terrestrial digital TV standard that tends to consume less power than its predecessor, the DVB-T standard, and generally allows the receiver to move freely while receiving the signal transmission, thereby making it ideal for cellular phones and other mobile devices to receive digital TV broadcasting over the digiTV network, and hence without having to use cellular telephone networks.
In mobile TV Digital Video Broadcasting—Handheld (DVB-H) systems such as DVB-H (ETSI EN 301 192), encoded video is broadcast over Internet Protocol (IP) packets. Encoded video bytes from a video decoder are mapped into variable length IP packets called IP datagrams. The IP datagrams are then mapped into sections where each datagram is pre-pended with a 12 byte section header and post-pended with a 4 byte section Cyclic Redundancy Check (CRC). Sections are then mapped on fixed length MPEG-2 Transport Stream (TS) packets of length 188 byte each. Generally, each TS packet has a header of 4 or 5 bytes. This procedure is typically referred to as Multi Protocol Encapsulation (MPE) and is illustrated in FIG. 1.
In order to protect the IP datagrams, a Reed Solomon (RS) Forward Error Correction (FEC) code may be applied to the IP datagrams. This is illustrated in FIG. 2, where IP datagrams are arranged column-wise in a matrix and then RS coding is applied row-wise to obtain FEC sections. This operation is called MPE-FEC. The thick arrows in FIG. 2 represent the direction of filling the columns of the table. For example, the arrows indicate that data is written from top to bottom in the table. After MPE-FEC, the IP datagrams are encapsulated into TS packets as depicted in FIG. 1. The FEC columns are also encapsulated into TS packets by mapping each FEC row into a section and then mapping FEC sections into TS packets.
FIG. 3 shows the architecture of a DVB-H transmission system 300. Here, one may notice that MPE-FEC provides protection to the IP datagrams. However, it generally does not provide any protection to the section headers, section CRC, Program Specific Information/Service Information (PSI/SI) sections, and the identifiers of different TS packets of different DVB services that get multiplexed into one TS. Typically, each DVB service has a unique TS identifier that is sent in the header of its TS packets, called the Packet Identifier (PID).
FIG. 4 shows the architecture of a DVB-H receiver 400 that extracts IP datagrams for a desired channel from the DVB-T signal. The DVB-T signal is decoded using a demodulator 410 that extract TS packets. At a very low signal-to-noise ratio (SNR), the TS packets can contain several errors. In general, such errors could be corrected by the MPE-FEC RS decoder 414 that can correct up to 32 random byte errors out of each 256 bytes in every row of the MPE-FEC frame shown in FIG. 2. However, the errors in the TS can cause the three blocks 412a, 412b, 412c in FIG. 4 to completely fail, thereby generating many more errors than the MPE-FEC RS decoder 414 can correct.
For example, the following three scenarios can cause several catastrophic errors; for example: (1) Errors in the PID of TS packets can cause the TS demux PID filter 412a to drop packets of the desired channel. Furthermore, it could case undesired TS packets to be passed incorrectly. (2) Errors in the TS packet header can cause dropping complete or parts of the desired MPE and FEC sections. (3) Errors in the desired section header can result in complete sections to be dropped or could cause sections to be written to the wrong location in the MPE-FEC table shown in FIG. 2. (4) Errors in the TS packets can prohibit the receiver from extracting the PSI/SI sections correctly. Any of the above errors can cause the MPE-FEC operation to fail completely to correct the errors introduced in the TS due to channel noise. Upon error correction, the IP datagrams are transmitted to an IP demux 416, which then extracts the desired IP datagrams to an IP decapsulator 418, which then decapsulates the video (bytes) to a video decoder 420, which transmits the audio/video content. Accordingly, there remains a need for a technique to allow a DVB-H receiver to avoid such catastrophic errors.
In view of the foregoing, the embodiments herein provide a data transmission method for DVB-H signals for enhancing data robustness of a DVB-H receiver in additive white Gaussian noise (AWGN) channels, and a program storage device readable by computer, tangibly embodying a program of instructions executable by the computer to perform the method, wherein the method comprises transmitting IP datagrams from a DVB-H transmitter to the DVB-H receiver; applying a MPE section and a FEC section to the transmitted IP datagrams; mapping the transmitted IP datagrams to TS packets; aligning boundaries of the transmitted IP datagrams to a given number of TS packets; fixing a size of the IP datagrams to a known value at the DVB-H receiver; and extracting the IP datagrams from the DVB-H receiver.
Preferably, the extraction of the IP datagrams from the DVB-H receiver occurs absent information provided in MPE-FEC section headers and information provided in headers of the TS packets. Moreover, the IP datagrams and the FEC sections are preferably of fixed length. Additionally, the length of the IP datagrams is preferably fixed to the same length of the FEC sections. Furthermore, the size of the IP datagrams are preferably transmitted to the DVB-H receiver. Also, knowledge of the fixed length of the IP datagrams preferably allows the DVB-H receiver to deduce section start address of all IP datagram sections. Preferably, Delta-t information corresponding to the IP datagrams sections is derived by averaging different values of Delta-t sent over different MPE and FEC sections.
The method may further comprise selecting a fixed length of all IP datagrams to fit exactly a fixed integer number of the TS packets. Moreover, the method may further comprise grouping the TS packets into units of a predetermined number of packets (K), wherein each K packet group comprises a same PID. The method may further comprise repeating each PSI/SI TS packet K times approximately every programmable period of time. Preferably, the method further comprises filtering the TS packets based on a PID of K consecutive TS packets.
Another embodiment provides a system for data transmission for DVB-H signals for enhancing data robustness of a DVB-H receiver in AWGN channels, wherein the system comprises a DVB-H transmitter adapted to transmit IP datagrams to the DVB-H receiver; a decoder adapted to apply a MPE section and a FEC section to the transmitted IP datagrams; logic circuitry adapted to map the transmitted IP datagrams to TS packets; align boundaries of the transmitted IP datagrams to a given number of TS packets; and fix the size of the IP datagrams to a known value at the DVB-H receiver; and a modulator adapted to extract the IP datagrams from the DVB-H receiver.
Preferably, the extraction of the IP datagrams from the DVB-H receiver occurs absent information provided in MPE-FEC section headers and information provided in headers of the TS packets. Moreover, the IP datagrams and the FEC sections are preferably of fixed length. Furthermore, the length of the IP datagrams is preferably fixed to the same length of the FEC sections. Preferably, the size of the IP datagrams are transmitted to the DVB-H receiver. Additionally, the DVB-H receiver may comprise a PID filter adapted to filter the TS packets based on the PID of a predetermined number (K) of consecutive TS packets.
These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.